Abstract: An optical beam phase shifter includes a liquid crystal cell having an optically-transparent common electrode on a first window and a multiplicity of parallel stripe electrodes on the second window. A multiplicity of control signals are applied between the individual stripe electrodes and the common electrode, thereby creating local variations of the refractive index of the liquid crystal molecules, which variations cause differential phase shifts across the cross section of a light beam incident thereon. The control signals are applied to contact pads affixed to an external surface of the liquid crystal cell, which contact pads underlie a plurality of the stripe electrodes. A multiplicity of conductors extend through the second window to couple the control signals to the stripe electrodes. In the first embodiment, the stripe electrodes are optically-transparent, and the incident beam is reflected from the contact pads.

Abstract: A timing recovery apparatus for a burst mode communication receiver. The apparatus provides for optimum sampling and digitizing of received data at a plurality of data rates. In particular, a VCO is phase-locked to a local frequency reference prior to data being received. A reference timing preamble transmitted prior to the data is filtered and fed to the VCO causing it to injection lock such that the VCO becomes phase aligned with the preamble. The VCO is then permitted to "free run" during data transmission and continues to operate at substantially the same frequency. A synchronous divider and multiplexer, responsive to the VCO, allows selection of sampling clocks for the plurality of data rates. The divider is forced to a known state during VCO injection locking, to assure that the sampling clocks have maintained the proper phase for optimal sampling at the corresponding data rate. Further, means is provided to monitor the frequency of the VCO.

Abstract: An optical time delay unit for use in an optical phased array beam-steering system includes a switchable polarization rotator in conjunction with Brewster plates and mirrors to form electrically-selectable optical paths of different lengths. The switchable polarization rotator is aligned with the optical beam and is responsive to a control signal for varying the polarization of light passing therethrough. The Brewster plates receive the light passing through the first polarization rotator and are transmissive to a first polarization and reflective of a second. The transmissive and reflective paths are of different lengths, and are recombined at a second Brewster plate. The original polarization may be restored by a second polarization rotator. A plurality of time delay units may be cascaded to permit selection from among many paths of various lengths. In a preferred embodiment, the polarization rotators include liquid crystal cells having nematic phase molecules.

Abstract: A magneto-optic disc recording system includes an E-shaped electromagnet for providing magnetic biasing selectively for the recording and erasing processes. The middle arm of the E comprises a first pole piece and is positioned radially with respect to the disc rotation, on the opposite side of the disc from, but aligned with, the path of radial motion of the focused recording/erasing light beam. The other arms of the E, parallel to the middle arm, comprise second pole pieces opposite in polarity from the first pole piece, and are positioned adjacent the disc recording surface on the opposite side of the disc from the middle arm. Two shoes of a magnetic material, coupled to the optical translation stage, provide a magnetic circuit between the respective second pole pieces and the area surrounding the objective lens focusing light on the disc recording surface, relaying a substantially vertical magnetic field through the disc at the point of incidence of the focused light beam.

Abstract: A magneto-optic disc recording system includes a cylindrical permanent magnet for providing magnetic biasing selectively for the recording and erasing processes. The magnet is positioned radially with respect to the disc rotation, on the opposite side of the disc from, but aligned with, the path of radial motion of the focused recording/erasing light beam. The poles of the magnet are diametrically opposed, and the magnet is axially rotatable. Circular eddy currents, induced by the magnetic field of the magnet on the surface of the rotating disc, generate a second magnetic field which opposes the field of the magnet, thus impelling rotation of the magnet. A stopping mechanism stops the rotation of the magnet with one or the other of its poles adjacent the disc, such that either a recording or erasing magnetic bias is selectively provided to the recording region.

Abstract: The range of a target is determined by imaging an illuminated spot on the target onto a detector surface by a focusing lens. The detector is positioned away from the focal point of the image of the illuminated spot, so that the image appears as a blurred circle. The range of the target is uniquely determined by the diameter of the blurred circle. In one embodiment the detector surface comprises a relatively large area having a narrow central area within two parallel boundaries equally spaced from a line representing the locus of the centers of the images on the detector surface. The diameter of the blurred circle can be determined by comparing the light energy received in the narrow central area of the detector with the total light energy received by the detector.

Abstract: A frequency division multiplex communications system groups a plurality of communications terminals such that they are coupled onto the communications bus at a single node. Each terminal comprises a fixed-frequency receiver, a frequency-agile transmitter, or both. Each receiver in the system is tuned to a different carrier frequency. Furthermore, the receivers grouped at each node are tuned to carrier frequencies within narrow frequency bands, typically within 2.5 percent of a center frequency, with no overlap between the frequency bands of the several groups. Using this configuration, only one receiver amplifier, one preselector bandpass filter, and one transmitter low pass harmonic filter are required for the plurality of terminals within the grouping.

Abstract: A temperature-controlled thermoelectric cooling system regulates the flow of electric current into the thermoelectric cooler in order to maintain a desired cold-side temperature without directly measuring the temperature of the device affixed to the cold side of the cooler. The system includes an apparatus for periodically interrupting the current flowing to the cooler, and during these interruptions measuring the open circuit voltage across the cooler induced by the temperature difference between the hot and cold sides. Computational means use this voltage measurement in conjunction with the temperature of the hot side of the cooler to determine the cold side temperature. From the cold side temperature determination, a controller regulates the current flow to the cooler to maintain a desired cold side temperature.

Abstract: An apparatus for selectively switching between either of two RF clock signal sources utilizes field effect transistors (FET's) as the switching elements. The FET's are driven at their respective base electrodes by complementary signals from open collector logic gates to provide signal source selection. In the event of loss of power to the RF switch, the energy from the RF signal passing through the previously selected switch path provides a positive (enabling) bias to the FET's in that path and a negative (disabling) bias to the FET's in the other path, thereby maintaining the selected path. The open collector logic gate circuits appear as open circuits when power is lost. During normal powered-on operation, the selection logic overrides the RF signal energy biasing circuits.

Abstract: A multiple track playback headwheel is disclosed for use in a helical scan optical tape recording system. The headwheel includes optical diffraction gratings at the center of rotation of the headwheel positioned normal to the rotational axis. A collimated light beam supplied from a laser external to the headwheel, directed along the rotational axis of the headwheel, is split into a plurality of beams by the gratings. The plurality of beams are imaged at the entrance pupil of the playback objective lens which focuses the beams to diffraction limited spots on the surface of an optical tape having information recorded thereon. The illuminated spots are reflected back through the objective lens and are formed into beams which are directed to an information and tracking detecting apparatus and to a focus detecting apparatus.

Abstract: A passive, single cable, local area network system includes two directional couplers at each cable tap to provide bi-directional communications for each communications terminal. Each coupler introduces some amount of signal power loss through the cable such that the signal power level between any two communicating terminals depends on the cable distance between them, measured in number of intervening cable taps. Selectable attenuators are provided between the directional couplers and the corresponding communications terminals to virtually equalize the signal power level between any two terminals. The value of attenuation is selected according to a relationship including the number of cable taps in the system, the signal power loss along the cable introduced by each directional coupler, and the ordinal number of the corresponding terminal from the cable termination in the direction toward which the terminal's directional coupler communicates.

Abstract: In an optical disc player having multiple read/write stations, the shock and vibration which is induced by the operation of loading one disc cartridge onto the turntable of one station may disrupt the recording/playing process in another station. The present invention discloses an apparatus and method for cushioning the shock of the loading process. As the cartridge is being loaded, pressurized air is supplied through orifices in the turntable reference plate to reduce the shock throughout the system. The air between the moving cartridge and the reference plate acts as a spring and damper to reduce the shock of the load cycle. In one embodiment, the pressurized air is supplied through the same orifices which are subsequently used to draw a vacuum which retains the cartridge against the reference plate.

Abstract: A circuit coupled between an indicating pushbutton panel switch and a software-programmable processor permits program control over the effect of switch actuation and over the illumination of the indicators. The processor can disable the switch function, blanking the indicators; it can accept a manual actuation of the switch, changing the illumination; it can reject as invalid a switch actuation within a multiple-switch field, retaining the current illumination; and it can alter the illumination in the absence of switch actuation. In one embodiment the signals providing the switch and indicator status are channeled into a serial data stream and transferred to the processor input register.

Abstract: A protective cartridge is provided for a disc record used in an optical playback system. The protective cartridge is provided with finger members to suspend the disc record in the cavity of the cartridge so that the information bearing surfaces of the disc record do not touch the inside surfaces of the cartridge. When the record package is in storage, the finger members are biased to engage the outside rim of the disc record. Tapered pins provided on the optical player disengage the finger members to permit the disc record to rotate in the optical player.

Abstract: A high-speed sampling head is disclosed which provides a transformer to isolate the sampling pulse source from the RF signal line to be sampled. The pulse width limitation of the transformer is overcome by propagating balanced forms of the pulse along a length of transmission line which enable unbalanced components of the sampled waveform to be propagated back along the transmission line, where the unbalanced components are detected and measured. The trailing edge of the sampling pulse passing through the transformer terminates the signal detection.

Abstract: An attenuator for high-power, low frequency RF signals including two .pi.-section low-pass filters is well matched to the transmission line characteristic impedance. Each of the four loss branches of the attenuator includes a power resistor and a PIN diode. The attenuator is made electronically variable by controlling the dc bias across the PIN diodes, which respond to increased voltage by exhibiting lowered resistance. At any setting of the dc bias, only a fraction of the attenuated RF power is dissipated by the diodes. When the bias voltage is tuned for high attenuation, virtually all of the power is dissipated by the power resistors.